By By Nancy Kramer - Victoria County Master GardenerEdited by Charla Borchers Leon
June 6, 2013 at 1:06 a.m.

2012 Texas Superstars

The Texas Superstar designation is only awarded to those plants that have been tested all over Texas and are proven to be successfully grown with little water, fertilizer, pesticides and time invested in them.

• Globe Amaranth (Gomphrena globosa) Fireworks - A new globe amaranth, both heat- and drought-tolerant. Older varieties and some new have also been named Texas Superstars. http://today.agrilife.org/2012/05/21/gomphrena-superstar-2012/

• Lowrey's Legacy Cenizo - A sage named after a horticultural hero, compact and cycles in and out of bloom better than other sages. http://today.agrilife.org/2012/06/27/lowreys-legacy-superstar/

Many times, gardeners desire small container plants on their patio or balcony or even around their pool. The Rio Mandevilla Texas Superstar, which was announced in June of last year, provides just that in a burst of warm tropical colors, including pink, hot pink and deep red, in trumpet-shaped flowers.

Tropical plants for way down south

Before you start to think, "How can a sub-tropical plant be grown anywhere except in Zones 9-11?" consider that this plant is designed to be grown in a container rather than the landscape, which enables you to protect it in the winter.

The more familiar Alice Dupont mandevilla has been popular for years but grows to be very large (up to 15 feet) and requires a trellis for vining. The other mandevillas are almost impossible to move around easily when cold weather threatens.

Dipladenia Rio Genus bred to stay compact

The Rio Mandevilla series are scientifically named Dipladenia sanderi and are in the same family as oleander, plumeria, allamanda and the desert rose. They have smaller, glossier leaves with a lot less twining than the typical Mandevilla splendens or Mandevilla x amoena.

They usually grow to only about 1 to 2 feet tall and wide and won't need trellises like with the typical un parasol mandevilla, which grows 12 to 15 feet or more.

The Texas Superstar Rio Mandevillas are bred to stay compact. This makes them more suitable for growing in containers or even planting them in the landscape in early summer and growing them as annuals.

Three dipladenia in Rio Mandevilla series

Rio pink, Rio hot pink and Rio deep red mandevillas will provide lots of blooms with 12 hours of light each day. They have beautiful, 3-inch trumpet-shaped flowers and bloom well in full sun to part shade. They do best with a bit of afternoon shade in the hottest part of the summer.

To get the full-blooming effect, AgriLife Extension recommends use of a slow-release container fertilizer, (18-6-12 or 20-10-20) every three months during the blooming season. Discontinue this feeding in the winter.

You can also trim it back in the winter to make it more manageable, but don't trim on it in the spring, or you'll cut off the new growth that will produce the flowering.

When planted in containers, use a good potting mix in a pot no larger than 20 inches with good drainage. They can stand drying out some but don't like staying over-moist all the time.

In the landscape, they will do best in soil with good drainage and high organic matter. When you water them, be sure to spray off the leaves, too. Mulching is desirable to keep them from drying out too much.

Layering great way to propagate more

Last year, when I bought my tiny start of the Rio deep red dipladenia, I repotted it in a 10-inch white pot and placed it in a special bed under a large, tropical spicy jatropha.

Since it was very well protected, and we only had light freezes in the Victoria area in 2012-13, my little 6-inch plant grew to 12 inches and naturally trailed over the edge. This trailing led to a small part of it reaching the ground. I threw some soil over that part, and it has taken root.

I can easily place that small, new plant in another container soon. Leaving it out in its pot all winter is most likely only possible in deep South Texas and not in all areas of Texas. It will need winter protection in colder parts of our state.

Traditional propagation also works well

Dipladenia can also be propagated by taking tender stem cuttings. Trim it back to about 6 inches where new leaf growth occurs at the top, remove the lower leaves, dip in rooting hormone and place it 2 inches deep in potting mix in a small container.

Water well, let drain and cover with plastic to create a greenhouse effect. Place in indirect sunlight in 70-75 degree temps. It will take about four weeks to root new Rio Mandevilla.

No pesticides generally needed

Infrequently, some of the pests that may affect the Rio Mandevilla are aphids, mealy bugs, spider mites or white flies. Check for these pests and spray off with a stream of water or use pesticide as necessary. The dipladenia is not prone to any disease if you avoid cool, wet growing conditions.

I'll take one of each

If you have a small area and desire a compact mandevilla in rich, tropical colors, the Rio Mandevilla is the plant for you. I always say, "I gotta have one of each."

Where would one, or all three, fit in with your favorite container plants?

The Gardeners' Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas AgriLife Extension - Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at VictoriaAdvocate.com.